1. Field of the Invention
This invention relates to apparatus for severing gobs from one or more streams of molten glass, in which the separation of each gob is effected by a pair of shear blades, wherein the shear blades of the pair or each shear blade pair are arranged on respective associated, pivotally mounted shear arms, and wherein the pivotal movement of the two shear arms is synchronized by means of a gear mechanism with the pivotal movements being produced by the driving of one of the shear arms by a drive means.
2. Description of the Prior Art
In one known apparatus of this type, German Auslegeschrift 28 18 234 B1, the electrical drive 1 rotationally drives a cam plate 2 having an arcuate groove 13. In the arcuate groove 13 runs a roller 3 of a lever 4 which is secured to the pivot shaft of one arm 5 of the shear arms 5, 8. The arcuate groove 13 is so formed that the shear arms 5, 8 maintain the most favorable speed for the individual sections of a working cycle corresponding to a working sector (360.degree.-.alpha.) and are stationary when traversing a dead period sector .alpha.. In the dead period sector .alpha. the cam plate 2 is either arrested or rotated more slowly for the purpose of the temporal positioning. Being tied to the course of the arcuate groove in the working sector is disadvantageous since it is expensive and not very flexible. The switching off or slowing down of the speed of rotation of the drive in the dead period sector .alpha. means additional expense.
From U.S. Pat. No. 3,736,826 it is known to drive a crank arm 38 by a hydraulic rotary drive 50, and by means of a gearwheel pair 46, 48 to drive a further crank arm 40 in the opposite sense. Eccentric pins on the crank arms 38, 40 drive respective coupling rods 34, 36 which are linked respectively to one of the shear arms 28, 30. This apparatus is expensive to construct and difficult to control from a technical point of view.
From German Auslegeschrift 1,922,247 it is known to provide mounting brackets 32, 52 which can be adjusted in the circumferential direction of a feeder spout 12.
In another known apparatus, U.S. Pat. No. 2,472,560, a pneumatic-mechanical drive for the shear arms 1, 2 is used. The one shear arm 2 is connected by means of a coupling rod 14 to a pivot lever 12 with a cam roller 11. The cam roller 11 runs on a rotating cam track 10a, 10b on which is coaxially arranged a further rotating cam track 50 for the actuation of a pneumatic control valve 36. The control valve 36 powers, by means of a conduit 51, 52, a chamber 17b of a piston-cylinder unit 17 with compressed air, with the piston rod 18 of the unit being coupled to the other shear arm 1. Thus, the force for the closing of the shear blades 7, 8 is generated by the piston-cylinder unit 17, and the course of the closure movement is controlled mechanically by the cam track 10b. In addition to this, the piston-cylinder unit 17 always keeps the cam roller 11 in contact with the cam track 10a, 10b. However, this known apparatus is expensive and fairly inflexible. With relatively high cutting rates of, for example, up to about 200 cuts per minute, the known drive is overloaded. Moreover, the working stroke of the shear arms is the same as its servicing stroke for the exchange of the drop ring, and is therefore undesirably large.
From U.S. Pat. No. 2,977,718 there is known an apparatus which uses a pneumatic-hydraulic drive. This requires high circuit expenditure and is likewise not suitable for the higher cutting speeds.
In another known apparatus, U.S. Pat. No. 2,678,519, each of the two shear arms 1, 2 is separately driven in the same manner, and indeed by means of a coupling rod 16, 17, a crank pin 18, 19 with crank 20, 21 and crank shaft 22, 23, a pinion 28, 29 and a gear rack 30, 31, which are displaceable by pistons 33, 34 of pneumatic cylinders 10, 27. The control of the pneumatic cylinders 10, 27 is effected by means of cams 109, 137, 138 and a number of valves of a pneumatic circuit. Here again, the expense is considerable and the flexibility is small.
From British Patent 688,803 there is known an apparatus in which both shear arms 1, 2 are drivable respectively by means of a toggle link 10, 11 through the piston rod 12, 13 of a common double-acting pneumatic cylinder 14. By this means the configuration of the movement of the shear arms cannot be reproduced. The length of the shear arms must be adapted to the stroke of the cylinder 14. It is not possible to center the shear arms 1, 2 in relation to the axis of the drop ring.
It is an object of the invention to improve the apparatus of the type first referred to above.
This is achieved in accordance with the invention in that a crank having an eccentric crank pin is driven by said drive means, a coupling rod is coupled on the one hand to the crank pin and on the other hand to said one shear arm, the drive means is arranged on a carriage, and the carriage is displaceable substantially transversely to the length direction of said one shear arm.
In this way two gobs in the case of double mould operation, and three gobs in the case of triple mould operation, of molten glass can be severed from the associated streams substantially simultaneously. Correspondingly, a number of shear blade pairs are then arranged on the respective shear arms with a spacing equal to the spacing of the streams. Preferably, the crank performs a complete rotation through 360.degree. in each working operation. The cutting stroke can be changed in a particularly simple manner simply by adjusting the effective crank radius. In order that the operation is not asynchronous, the crank is brought to a standstill after each working operation and is maintained in this stationary state during a minimum waiting period of for example 20 ms. For a given movement period of the shear arms during one working cycle of for example 250 ms, the length of the waiting period depends upon the cutting speed, i.e. on the number of shearing cuts per minute. The crank drive is designed as a non-linear transmission gear system and permits one to start the drive in a relatively lightly loaded manner. Thus, its own acceleration is facilitated for the drive when starting up and the energy requirements are reduced. The use of the carriage brings the particular advantage that one keeps the working stroke of the shear arms to a minimum and thereby on the one hand reduces working energy and on the other hand can increase the maximum possible working speed. Also, the carriage makes it possible to have a very simple and rapid opening of the shear arms, even beyond the opened position relevant to the working stroke. This further opening is desirable for example if servicing or replacement of the drop ring of the feeder bowl has to be undertaken. The drop ring and its surroundings can then be made accessible for the purpose of servicing in a very rapid and simple way. The further opening of the shear arms into their servicing position can also take place automatically upon shutdown of the drive. For this purpose the control of the drive system generates a starting pulse for a further control for the return drive of the carriage. The shear arms then remain in their further opened security setting until the fault of the drive has been overcome. In this way the shear blades cannot collide with the glass streams.
In a preferred embodiment of the invention, the carriage is guided on guide rods of bracket means, and the bracket means is adjustable circumferentially of a feeder which supplies the glass stream or streams. According to this embodiment the bracket means and consequently the carriage and the drive for the shear arms can be adjusted easily and rapidly to the optimum angular position relative to the shear arms, and indeed in dependence upon space requirements in the circumferential direction either on the one or on the other side of the shear arms. Also, the shear arms themselves can be adjusted in a manner known per se in the circumferential direction relative to the feeder bowl, at least if one is talking about multiple shears which are designed to sever gobs from more than one stream. The rotational position of the glass streams must be able to be adjusted to the glass forming machine which receives the glass gobs. The circumferential setting both of the shears and also of the bracket means with the drive is preferably effected by fixing these elements with hammer bolts in circumferential T-grooves of the feeder bowl. Preferably, two such T-grooves are arranged axially spaced from one another on the feeder bowl, so that one obtains a sufficiently rigid fastening of the shears and of the drive to the feeder bowl.
Preferably, the carriage is displaceable by at least one piston-cylinder unit which is supported on the one hand on the carriage and on the other hand is rigid with the apparatus. The piston-cylinder units are preferably double-acting units so that the carriage can be displaced in both directions by the driving force.
According to a preferred embodiment, the movement of the carriage in the direction of the shear arms for adjusting the overlap of the shear blades is limited by at least one stop element which is adjustable and is mounted to be rigid with the apparatus. Thus, the overlap of the shear blades can be adjusted in a particularly simple manner and very accurately. The overlap, i.e. the mutual overlapping of the shear blades of each paid of shear blades, should be kept as small as possible. The gobs should be separated cleanly from the stream. As soon as the shear is made, the shear blades should not unnecessarily overlap each other any further but should perform their return movement into the open position.
Preferably, the coupling rod is connected at its two ends to respective universal joints. This facilitates the height adjustment of the shears relative to the outlet of the orifice ring which permits the streams of molten glass to exit from the feeder bowl.
Preferably, the drive means comprises an electric servo-motor. This gives a particularly advantageous drive mechanism. In particular, one can use a three-phase servo-motor with feedback as the servo-motor, the control of which is freely programmable in respect of the speed-rotary angle-path. Thus, by pre-programming, the shear arms can in any angular position be provided with the optimum speed values, and indeed, if need be, with different speed values for the closing and opening movements of the shear arms. By the inventive use of an electric servo-motor, the overall cycle duration which, as mentioned above, can amount to 250 ms, can be reproduced in practice with an accuracy of for example approximately 1 ms.
The drive means preferably comprises a gear mechanism connected between the servo-motor and the crank. In this way one then has more freedom of choice in the layout of the speed of the servo-motor.
Preferably, a pneumatic piston-cylinder unit is connected on the one hand to the other of the shear arms and on the other hand to a bearing which is rigid with the apparatus. With such a piston-cylinder unit one is talking in effect about an air spring. The gear mechanism for synchronizing the shear arms preferably consists of toothed segments which mesh with each other and which are provided coaxially in relation to spaced pivot shafts of the shear arms. The air spring keeps the teeth of the toothed segments permanently in contact with each other as much as possible. In this way one is careful with the toothed segments, the drive means is freed from avoidable load and the positioning of the shear blades is improved.